In all the talk of graphical downgrades no one seems much preoccupied with 'why?'. Why build something and then proceed to tear it down, piece by piece, in the hope that ever more diminished expectations about the final product won't be severe enough to...
Corral the zombies, then shoot them when they're in a big group.
There are jumps in some of the arenas, but it's usually best to keep your wheels on the ground.
Obstacles will flash red if they're about to pop out of the arena floor.